Screw thread configurations for the screw element of dental implants are known from a number of publications in the state of the art. Thus DE 201 13 254 U1 describes a cylindrical screw implant in which, starting from a cylindrical anchoring head, the screw thread core conically tapered in diameter from crestal to apical while the self-cutting outer screw thread has a constant outer diameter over its length. Because of the fact that the thread becomes increasingly deeper from apical to crestal, at the apical end the implanted screw element forms gaps between the inner wall of the cylindrical final bore in the jaw bone and the thread core which is detrimental on medical grounds.
With the shape of the screw element known from DE 37 35 378 C2, the screw thread has an outer diameter which is constant over the greater part of its length for the thread core and outer thread portion. Only toward the apical end of the screw element does the thread core and outer thread have a slightly conical configuration. Because the greater part of the thread length has a constant outer diameter, this earlier dental implant upon screwing requires relatively greater force with increasing depth to which the implant is screwed into the jaw bone which can result in a relatively strong trauma to the impacted bone tissue.
DE 36 42 901 A1 discloses a special thread for a dental implant which has a relatively strongly conically tapered thread core combined with an outer thread up to a short conical run to the apical end with a constant outer diameter. Here as well the problem arises in that the greatest thread depth is in the region ahead of the apical end.
EP 0 282 789 B1, finally relates to a self-cutting bone implant for dental purposes which can be screwed into the bone and which has a thread configuration which corresponds to that of the first mentioned utility model. To the extent that also combines a conically tapered thread core with an outer thread whose outer diameter is constant, the outer diameter especially is equal to the outer diameter of the cylindrical post anchor.
As further alternatives for the screw element, a screw pattern is claimed in this publication whereby the outer diameter of the outer thread which is equal to the diameter of the cylindrical anchoring head, constantly is reduced toward the free end of the core and a conical thread core is provided. In other words, a conically tapering outer thread is combined with a core which is also conical. As a result of the continuous diameter reduction and the omission of any cylindrical segments in the thread core and/or outer thread, the stability and intrinsic bond between the implant and surrounding bone tissue can be affected.
As can be deduced from the state of the art represented by the publication but not explicit therefrom but known from the actual practice employing dental implants, the bores provided in the jaw bone in all cases have diameters such that the outermost tips of the screw thread rib will penetrate into the bone tissue. The thread turns can be then formed as recesses which grow to stabilize the seat of the implant in the bone tissue. It is desirable to improve such dental implants, especially as to their primary stabilities.